The invention relates to a liquid filter, especially an oil filter for an internal combustion engine, with a bypass valve for the liquid to be filtered in which the bypass valve and a valve seat are mounted in the area of the end plate of the filter insert. In addition, the invention relates to a filter insert that is suitable for installation in a liquid filter of this type.
In liquid filters with cylindrical filter inserts, it is known to house a bypass valve in the area of one of the axial end plates. This is to assure that liquid will still flow in case the throughput resistance at the filter element increases to an unacceptably high level. In such a case, the liquid supply is ensured for the liquid system by opening the bypass valve.
A liquid filter with a bypass valve is disclosed, for example, in German Patent No. DE 196 05 425 C2. FIG. 2 of this patent shows a liquid filter in disassembled condition. A support member 15 is provided in the housing on which a valve body 9 that is biased by a spring 12 is mounted. When the filter element 3 is installed in the filter, a valve seat 14 is found in the end plate 5 associated with the filter element. This provides a cost-effective structure for the bypass valve.
However, when the filter element is changed, only the valve seat 14 included in filter element 3 is changed. Valve body 9 remains in the support member, which is designed so that it is fixed to the housing. Therefore, in the course of filter use, the valve body 9 is exposed to wear and soiling. Consequently, the valve body can lose its seal integrity, especially in modern diesel engines, because of the deposit of soot particles, so an undesirable, unfiltered secondary current of lubricating oil develops at the bypass valve. Because of this, the quality of the lubricating oil is impaired, which either endangers the function of the internal combustion engine or means that more frequent oil change intervals are necessary.
In order to prevent a malfunction, valve body 9 can also be changed at each filter change. However, this creates increased installation effort and produces a source of possible defects because a technician could forget to replace the valve body.
It is therefore the object of the invention to provide a liquid filter with a simply structured bypass valve.
It is also an object of the invention to provide a liquid filter with a bypass valve which is reliable in function over the entire service life of the filter.
These and other objects are achieved in accordance with the present invention by providing a liquid filter having a housing structure with an inlet and an outlet for the liquid to be filtered, in which a cylindrical filter insert is installed, which has a bypass valve in the area of one of the end plates, and in which the bypass valve comprises a valve body which is movably mounted in the filter insert and which in a closed state contacts a valve seat integrated in an end plate of the filter insert; and a support member is mounted on the housing for supporting a spring that is compressed against the installed valve body to urge the valve body against the valve seat.
The liquid filter according to the invention has a housing structure in which a filter insert is installed in a known manner. The housing structure can represent a separate housing or an integrated component e.g. of an internal combustion engine. The filter insert is designed so that it is cylindrical, while the bypass valve is housed in the area of one of the end plates of the filter insert. In this process, the valve seat is housed in a known way in the end plate. On the other side, in the housing structure a support member is provided that is used to install a spring that is responsible for pre-stressing or biasing the bypass valve whereby the opening pressure is defined.
The liquid filter is characterized in that the valve body is also mounted in the filter insert so that it can move and in such a way that during replacement of the filter element it can also be replaced. This means that an unacceptably high degree of soiling of the valve body, e.g. by soot deposits, is prevented since it is regularly changed along with the filter insert. The required high reliability of the liquid filter is thus attained.
The spring, which is preferably a coil spring of metal, remains in the support member when the filter element is changed. Because of this, the filter element can be designed so that it is free of metals, which makes is possible to dispose of the used filter element without difficulty, for example by incinerating the filter element.
In accordance with one advantageous embodiment of the invention, the valve body can move axially in the end plate of the filter insert. An axial stop for the valve body is provided in the opening direction of the bypass valve which limits the movement of the valve body away from the valve seat and assures that the valve body does not fall out when the filter insert is replaced. Alternatively, the valve body can be slightly oversized in relationship to its installation opening in the end plate so that it is prevented from slipping out during installation, but the axial movement capability for the valve function is still assured.
The axial stop for the valve body can advantageously be formed by resilient or elastic tabs. This makes the installation of the valve body in the end plate easier. During the installation, the resilient tabs move back and then prevent the valve body from falling out.
In accordance with another embodiment of the invention, the valve body can be manufactured at least partially of an elastomer. In this way, the sealing effect of the valve body on the valve seat, which is formed on the end plate, can be improved. For example, the valve body can be manufactured in a two-component injection molding technique in which an elastomer layer is formed on a surface of the valve body which engages the valve seat. Alternatively, the entire valve body can be manufactured of an elastomeric material.
In accordance with yet another advantageous embodiment of the invention, an intermediate piece can be mounted between the spring and the valve body which causes a transmission of force between spring and valve body when the filter insert is installed in the filter housing. The intermediate piece is especially advantageous if the entire valve body is manufactured of an elastomer. Because of the intermediate piece, the spring force can then be transferred to the valve body without damaging it. In addition, the intermediate piece can be used to secure the spring at its installation location.
The arrangement described above with intermediate piece can also be implemented with a liquid filter according to DE 196 05 425 C2. In order to prevent multiple use of the valve body when the filter insert is replaced, its function can be changed to that of the described intermediate piece by providing a suitably designed new valve body in the end plate of the replaceable filter insert. Thus, the former valve body takes on the function of force transmission between spring and valve body. The sealing function is transferred to the new valve body in the filter insert, which neither becomes soiled or worn and thus ensures reliable function of the bypass valve during further use of the liquid filter.
It is advantageous to simultaneously use the support member that serves for holding the spring as a support for the filter medium. This can be implemented if the filter element has flow that passes radially from the outside to the inside. Alternatively, the filter element can also have flow that passes from the inside to the outside. However, the support member must then be mounted outside the filter insert consistent with the required direction of action of the bypass valve, so the spring can develop its spring force from outside in the direction of the end plate of the filter element.
One advantageous design of the invention provides that, with a filter insert that has a radial flow from the outside to the inside, a passage in the filter insert which leads to the outlet of the housing structure and the bypass valve are arranged parallel to each other in one and the same end plate of the filter insert. In the case where the bypass valve is opened, the shortest distances can be realized in this manner, which prevents a soiling of the clean side of the filter element. In addition, a more compact structure of the liquid filter is possible because of this. In the structure described, it is advantageous to design the valve bodies with an annular or ring shape. The passage for the liquid filter outlet is then mounted on the inside and is surrounded annularly by the valve seat.
The housing structure of the liquid filter can advantageously be designed as a replacement for a disposable filter. This means that the filter insert in this housing structure can be replaced individually, but the entire housing structure can be mounted at the installation location instead of a disposable filter. In this way, for example, the disposable filters of older engine model series can be replaced by more environmentally friendly variations comprising reusable housings with replaceable filter inserts.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.